If someone configure IDLE to start a edit window by default, I believe
it should open only an edit window without starting shell window. This
has been the behaviour in previous version, but it is acting different now.

I looked into r71126 and I think this behaviour was changed there
unintentionally. Its log message doesn't seem to mention this change,
that is why I'm thinking this.

I agree on this. Unfortunately that change in r71126 wasn't commented on or documented in any way.

After looking through the code and experimenting a bit, I propose the following:

The "editor-on-startup" config option should be removed. Running IDLE without arguments should open a shell. If IDLE is asked to open any files for editing, it should open just editor windows. IDLE should open both a shell window and one or more editor windows only when explicitly asked to do so on the command line.

If this is done, the -e option ("open an editor") would tell IDLE to open an empty editor window if no files are asked to be opened for editing. If no other arguments are given, IDLE will open just an editor window (no shell window). The -i option ("open a shell") would tell IDLE to open a shell window even if asked to open files for editing.

I think this is more obvious and easier to work with. It will also make the command line argument processing code simpler. And as a bonus we remove a config option :)

Thoughts? Comments? If there is agreements I will work up a patch.

Keep in mind that, on OS X, there are two ways to invoke IDLE: one, by command line in a terminal window, and, two, by launching IDLE.app (explicitly, say by double-clicking on the app icon, or implictily, say by double-clicking on a .py file where IDLE.app is the default application for that file type).  With IDLE.app there is no opportunity for the user to specify command line options.  I suspect that on OS X IDLE.app is used far more frequently than the command line.

My question is, when IDLE is run without arguments (as is the case for IDLE.app), what is the benefit opening an empty editor window as opposed to a shell window?

In both cases if you just want to edit a file you must open it via the menus (e.g. File->Open or File->Recent Files), and an unused window is left open. On the other hand, if you do want a shell, having an empty editor window is useless. Therefore I think in this case it is always better to open a shell window.

The current behaviour on OSX for IDLE.app is to always open a shell window, and open edit windows for any files that should be opened during launch.

IDLE.app does not open an empty edit window, and I agree that this is sane behaviour.

One other thing that might be interesting to know: IDLE.app is already set up to open just a single instance of IDLE when users open python files from the Finder.

Attached is a patch to correct the existing bug as-is. 

Should the behavior of IDLE be changed as Tal suggests?

When I click r71126 it is mapped to bc084a97318b for #1529142
KBK msg85379 says "The -e option now only opens an editor window,"

I think I agree with Tal's suggestion as long as thing still work ok on Mac. It is trivial to open a new empty window from the shell.

I have not looked at the current patch yet.